The invention relates to a control apparatus of a laser diode for controlling a light emitting power of a laser beam which is irradiated from the laser diode to an optically rewritable or unwritable recording medium such as optical disk, magnetooptical disk, or the like and, more particularly, to a control apparatus of a laser diode whose light emission is driven and in which a cathode is connected to the ground side of a positive power source and an anode is connected to the plus voltage side of the positive power source through a control circuit.
In an optical recording and reproducing apparatus using an optical recording medium such as optical disk, magnetooptical disk, optical card, or the like, a laser diode is used as a light source, the light emission is controlled to a large write power in the writing or erasing mode, and the light emission is controlled to a small read power in the reading mode.
In the reading mode corresponding to a small power, a power level exists in a noise region of the laser diode and an S/N ratio of a reproduction signal deteriorates. Therefore, there is used a read modulating method such that the light emitting output is modulated so as to have a peak level exceeding a noise level at a frequency which is higher by one or more digit than a recording frequency and an execution power is suppressed within the noise region even when a peak power is high.
Further, in order to suppress a fluctuation of the light emitting power during the use of the laser diode, an automatic power control (hereinafter, abbreviated to "APC") is used, thereby controlling a light emitting power in the reading mode and a specific power (lowest power level when there is no light emission) in the writing mode to set reference values.
Generally, the laser diode has a unit structure such that it is packaged integratedly with a photodiode for monitoring. A negative power source is ordinarily used due to a diode connection in the unit.
In the field of a small disk apparatus, however, a positive power source is generally used and it is demanded that the small disk apparatus can be driven by the positive power source.